2011

ElasticSearch's new "Percolator" feature, which enabled to index queries and find which documents match them : instead of sending docs, indexing them, and then running queries, one sends queries, registers them, and then sends docs and finds out which queries match that doc.

2010

An interesting article from Lucid Imagination employee Mark Miller about Scaling Solr. It gives a lot of good practices and tips on how to get the best out of one indexing machine, and explains how to use Solr built-in replication system.